There is substantial evidence that the hormones gastrin, secretin, and cholecystokinin (CCK) exert trophic influences on normal stomach and liver. To date, however, little work has been done to investigate possible trophic influences of these hormones on carcinomas arising in these organs. The nude mouse is a unique experimental animal which is well-suited to study this question because it will readily accept subcutaneous xenografts of human and animal cancers. Human and animal carcinomas arising in stomach and liver and established by implantation in nude mice will be used to investigate possible trophic effects of the hormones gastrin, secretin, and CCK. After these tumors have been transplanted subcutaneously into nude mice, injections of gastrin, secretin, and CCK will be administered for specified periods of time and the growth of the tumors will be recorded. The animals will then be sacrificed and the effects of the hormones on tumor size, pattern of metastases, and hostology will be determined. Morphometric study of the tumor implants will be carried out, and determinations of DNA, RNA, and protein content of the implanted tumors will be done. Serological markers (carcinoembry onic antigen or alpha feto protein) will also be measured. These studies will: 1) establish whether gastrin, secretin, and CCK exert growth-modulating effects on these human andanimal carcinomas in the nude mouse model; 2) elucidate mechanisms involved in any trophic effect observed; 3) suggest potential roles for novel approaches to these diseases in man (including surgical procedures).